1. Field of the Invention
The present invention relates to a motor driving circuit.
2. Description of the Related Art
In electronic devices employing a disk medium such as portable CD (Compact Disc) devices, DVD (Digital Versatile Disc) devices, etc., a brushless DC motor (spindle motor) configured to rotate the disk is employed. In general, a brushless DC motor includes a rotor including permanent magnets and a stator including multiple phase coils connected in a star-winding manner. With such an arrangement, the electric current to be supplied to each coil is controlled so as to excite the coils, thereby rotating the rotor relative to the stator. In general, a brushless DC motor includes a sensor such as a Hall effect sensor, an optical encoder, or the like, in order to detect the rotational position of the rotor. A brushless DC motor is configured to apply a suitable torque to the rotor by switching the current to be supplied to each phase coil according to the position thus detected by the sensor.
In order to further reduce the size of the motor, sensorless motors have been proposed, which are configured to detect the rotational position of the rotor without involving a sensor such as a Hall effect sensor or the like (e.g., see Patent Documents 1 and 2). For example, a sensorless motor monitors the electric potential (which will be referred to as the “midpoint voltage” hereafter) and the back electromotive voltage (induced voltage) that occurs at one terminal of the coil, and detects the zero-crossing point at which the midpoint voltage and the back electromotive voltage thus monitored exhibit the same value.
Furthermore, a voice coil motor is employed to control a head included in a hard disk or the like. While the spindle motor is driven in a switching manner, the voice coil motor is driven in a linear manner.